Decreases in plasma volume (hypovolemia) elicit thirst and sodium appetite in rats. Only animals ingesting large amounts of water and saline solutions were found to repair their plasma volume deficits, thus demonstrating the important contributions of these ingestive behaviors to homeostasis. A close association was observed between plasma renin activities and plasma aldosterone levels, and between these changes and the observed drinking behaviors. These correlations are generally consistent with previous hypotheses that angiotensin and aldosterone are stimuli for thirst and sodium appetite, respectively, in rats during hypovolemia. However, four observations were in direct conflict with those hypotheses. First, hypovolemic rats given only water stopped drinking despite continued elevation of plasma renin activities. Second, nephrectomized rats drank water in response to hypovolemia as did intact controls despite the absence of increases in plasma renin activity. Third, the appearance of sodium appetite followed the increase in aldosterone levels by at least 6 hr. And, fourth, nephrectomized rats did not show sodium appetite during hypovolemia despite significant elevations in circulating aldosterone levels. These findings suggest that one must be cautious in attributing too much of a contribution of the renin-angiotesin-aldosterone system to thrist and sodium appetite of rats during hypovolemia.